/Engine/Source/Runtime/SlateCore/Public/Widgets/SWidget.h
Optionally, update the collapsed attributes (attributes that affect the visibility) of the children before executing the virtual ArrangeChildren function. The visibility attribute is updated once per frame (see SlatePrepass). Use the option when you are calling ArrangeChildren outside of the regularSWidgetPaint/Tick.
void ArrangeChildren ( const [FGeometry](API\Runtime\SlateCore\Layout\FGeometry) & AllottedGeometry, [FArrangedChildren](API\Runtime\SlateCore\Layout\FArrangedChildren) & ArrangedChildren, bool bUpdateAttributes ) const